The zigzag folding of sheets of paper is a technique that is frequently used after printing or reproducing large-format plans, technical drawings, blueprints, etc., in order to fold such sheets into a standard size that makes it possible to file them in a box file in such a way that they can be easily removed and/or unfolded. The zigzag folding of the sheet and if need be the lateral folding of the resulting zigzag-folded set has to be carried out in such a way that each information field situated in the bottom right-hand corner of the sheet for indicating the plan designation or drawing reference number appears on top of each sheet, on its uppermost fold, and that the lateral sheet edge adjacent to this information field protrudes sideways at the bottom fold of the zigzag-folded set, wide enough for a binding-margin.
To achieve this result through zigzag-folding sheets of large formats (larger than DIN A 4, i.e., larger than approximately 8".times.111/2"), the sheet that conventionally was spread out on the feeding channel with its printed side up has heretofore been fed into the zigzag folding apparatus with the binding-margin as the leading edge. Thus, the information field is situated at the back corner of the sheet, seen on the left in relation to a vertically illustrated feeding axis, and feeding or advance takes place along the axial direction of the bottom edge of the sheet or printed image, which edge connects between this sheet corner and the above named forward sheet edge. The sheet's bottom edge slides along a guide bar arranged at the left edge of the feeding channel. The generally desired reinforcement of the sheet margin and its perforation is carried out immediately before the sheet enters the folding apparatus.
The known zigzag folding process is electronically controlled in such a way that the bottom panel of the resulting zigzag-folded set is laid out with its printed side up as it leaves the folding apparatus, and each subsequent panel is laid onto the previous one in such a way that the uppermost panel with the information field is laid out printed side up in the same manner as the bottom panel. Thus the zigzag-folded set has at least two or a higher even number of fold edges, depending on the size of the sheet, running parallel to the binding-margin; the distance between these fold edges and the margin are determined automatically through conventional size-scanning of the sheet with sensors arranged within the feeding web and by a computer that controls the folding process accordingly and thus adjusts and determines the folding sequence.
If the printing or reproducing apparatus automatically delivers sheets of varying sizes with their bottom edges, abutting the guide bar arranged at the left margin of the feeding channel, the continued advance along this bar, creation of the binding-margin, and the zigzag-folding process can also become fully automatic.
However, if the sheet supply in the printing or reproduction apparatus is arranged separately by format in different stacks or rolls in such a way that each sheet is delivered automatically with its lower printed-image edge abutting at a guide bar arranged at the right-hand margin of the feeder web, the information field is situated in the right-hand forward corner of the sheet, and the sheet edge intended for the binding-margin is situated at the rear edge of the sheet. In this case the above described zigzag folding system would not result in a folded set meeting the aforementioned requirements, even if the computer were to be reprogrammed according to the altered initial position of the sheet. The information field would be on the top side of the bottom panel and would thus face inside the zigzag-folded set, while the binding-margin would be on the uppermost panel.